一种汽车的方向盘的直径为40厘米,它的周长和面积各是多少?
∵d=40cm,
∴S=πr2=400πcm2,
C=πd=40πcm.
答:它的周长和面积各是40πcm,400πcm2.
My mother often _____ me ____ housework on Sunday.
A. make… do B. makes …does C. makes …do
简述切片需要预结晶的原因?